Fluid heat apparatus

ABSTRACT

THE INVENTION PROVIDES A GAS-FIRED WATER HEATER COMPRISING A BURNER UNIT INCLUDING A MAIN BURNER AND A PILOT BURNER, A COMBUSTION CHAMBER AND A HEAT-EXCHANGER ASSEMBLY SEALED BY A CASING, TWO CONDUITS FOR ADMITTRING COMBUSTION AIR TO, AND EXHAUSTING CONBUSTION PRODUCTS FROM, THE COMBUSTION CHAMBER, A HORIZONTALLY DISPOSED BALANCED FLUE CONSTITUTED BY THE EXTREMITES OF SAID CONDUITS, AND AN EXTRACTION FAN INCORPORATED IN THE EXHAUST CONDUIT TO DRAW COMBUSTION PRODUCTS FROM THE CONBUSTION CHAMBER AND TO EXPEL SAID COMBUSTION PRODUCTS TO ATMOSPHERE THROUGH THE EXHAUST CONDUIT. PREFERABLY THE EXTRACTION FAN INCLUDES ELECTRICAL SWITCHING MEANS ADAPTED TO CONTROL THE COMBUSTION PRODUCTS EXTRCTION RATE OF THE FAN IN SUCH A MANNER THAT THE THROUGHPUT OF THE FAN REQUIRED FOR OPERATION OF THE MAIN BURNER IS REDUCED WHEN GAS IS SUPPLIED TO THE PILOT BURNER ONLY.

p 0, 1971 J. ROSIEK 3,606,150

7 FLUID HEAT APPARATUS Filed Aug. 6, 1969 2 Sheets-Sheet l MM BY 1M1wyumgm Sept. 2 0, 1971 Y os g 3,506,150

mun HEAT APPARATUS Filed Aug. 6. 1969 2 Sheets-Sheet W .BYMMJ ZZM MUnited States Patent Office 3,606,150 Patented Sept. 20, 1971 3,606,150FLUID HEAT APPARATUS Jozef Rosiek, Surhiton, Surrey, England, asslgnorto Potterton International Limited, London, England Filed Aug. 6, 1969,Ser. No. 847,939 Claims priority, application Great Britain, Aug. 15,1968, 39,031/68; May 2, 1969, 22,456/69 Int. Cl. F23n 1/02 I US. Cl.23620 7 Claims ABSTRACT OF THE DISCLOSURE The invention provides agas-fired water heater comprising a burner unit including a main burnerand a pilot burner, a combustion chamber and a heat-exchanger assemblysealed by a casing, two conduits for admitting combustion air to, andexhausting combustion products from, the combustion chamber, ahorizontially disposed balanced flue constituted by the extremities ofsaid conduits, and an extraction fan incorporated in the exhaust conduitto draw combustion products from the combustion chamber and to expelsaid combustion products to atmosphere through the exhaust conduit.Preferably the extraction fan includes electrical switching meansadapted to control the combustion products extraction rate of the fan insuch a manner that the throughput of the fan required for operation ofthe main burner is reduced when gas is supplied to the pilot burneronly.

This invention relates to a gas-fired water heater.

A known gas-fired water heater of the so-called balanced flue typeessentially comprises a burner unit, combustion chamber andheat-exchanger assembly sealed by a casing with respect to the room inwhich the heater is installed and having two conduits for admitting combustion air to, and exhausting the products of combustion from, thecombustion chamber, the external extremities of the conduits beingdisposed externally of the room closely and parallelly to one another ina common terminal unit so as to provide automatic draught compensationin accordance with varying wind conditions.

For many domestic gas-fired water heaters, especially those of smallmodern dwellings, it is desirable that the Water heater should be ofsmall overall dimensions to enable it to be sited in an unobtrusivemanner on a kitchen wall or under a working surface, for example. Oneknown such balanced-flue heater of the type described above achieves ahigh thermal output and compact dimensions by including a highefficiency heat-exchanger and electric fan means for forcing air intothe combustion chamber. The advantage of such forced-draught heaters ascompared with appliances that rely upon convected aid circulation isthat the cross-sectional areas of the inlet and outlet conduits isreduced.

However the above-mentioned heater essentially entails the use of aslightly pressurised combustion chamber and it is possible forcombustion ,(or fine) products to escape into the room if leakage occursin the sealed cas ing which surrounds the combustion chamber. Forexample, if the casing is constructed of sheet metal, leakage can occurif not all of the panels are accurately formed so that their abuttingedges do not produce the desired fluid-tight joint. Furthermore, leakageproblems can arise if access openings to permit the servicing ofinternal components are not provided with efficient sealing gaskets. Yetagain, if the casing is manufactured from steel sheet there is aninherent risk of corrosion which could perforate the casing thus toallow leakage into the room.

Furthermore when a heater of the type described above is used as a heatsource for a domestic or similar waterheating installation it isessential that some form of thermostatic control is incorporated toprovide a desired temperature. For example, if the heater is used purelyfor space heating purposes, a room air thermostat is usually provided tocut off the fuel supply to the burner when a predetermined airtemperature is attained. Although it is possible to provide modulationcontrol gradually to reduce the burning rate in accordance with thedemand for heat, conditions can prevail when a minimum burning rate isgreater than the heat loading, and in these conditions the thermostatcauses the burner to be cut off. Similarly, when the heater is used inconjunction with a combined space-heating and consumable hot watersystem it is usual to provide a hot water tank tempera ture-sensingthermostat to restrict the primary hot water flow when a desiredtemperature is attained; thus the heat load is reduced and when thelower limit of modulation is exceeded the fuel supply to the burner iscut off. Thus, it will be seen that under certain heat-load conditionsthe burner will be frequently extinguished and relit, even thoughmodulating controls may be employed.

It is usual practice in apparatus of the type described to connect theelectric fan in an electrical circuit containing electrical means forcontrolling the supply of fuel to the main burner in such a manner thatthe fan operates only when the burner is alight. This electrical meansconveniently comprises a solenoid-operated valve adapted to admit fuelthere-through when it is energised and to cut off the supply of fuelwhen it is de-energised. The pilot burner, which is connected to thefuel supply at a point upstream of the solenoid valve, is capable ofburning without artificial aid induction, and accordingly burnsirrespective of operation of the electric fan.

We have found that the above described apparatus suffers from evenfurther shortcomings. For example, an adequate amount of combustion airis not immediately available in the vicinity of the burner when the fuelvalve is opened. The effect of this is to creat unreliable and noisyignition. Furthermore, upon cutting off the fuel supply to the mainburner the supply of combustion air is also abruptly cut off with theresult that the system is not completely purged and thus certaincombustion products remain within the heater. During the resultantcooling of the heater the said products inevitably condense and causecorrosion and formation of solids to take place within the casing andflue passageways of the heater. A similar detrimental effect is causedby the combustion products from the continuously burning pilot burner.The thermal output of the pilot burner is insuflicient to cause asatisfactory convected air flow through the inlet and exhaust conduitsand consequently condensation takes place.

Particularly in the case of heaters having low-water capacity heatexchangers it is necessary to provide a safety temperature control meansto safeguard against the attainment of abnormally high temperatureconditions, for example, as may be created by failure of awater-circulating pump. This safety means comprises conveniently athermally sensitive probe situated within the heat exchanger and capableof breaking the electrical circuit to the solenoid-operated gas valvewhen a water temperature of say 200 F. is attained. During stand-byconditions, when the main gas burner, the water-circulating pump and thefan are not in operation, it is possible for the pilot burner, which maytypically be of 500 B.t.u./ hr. rating, to heat the small quantity ofstatic water contained within the heat exchanger. The effect of this,under certain ambient conditions, is to actuate the above mentionedsafety means and thus prevent future operathe above-mentioned leakageproblem by providing a gasfired water heater in which the interior ofthe casing is, in use, subjected to a slight negative pressure withrespect to ambient atmospheric air pressure.

It is a further object of the present invention to overcome theabove-mentioned thermal and chemical problems by ensuring that aircirculation continues within the relevant parts of the heater duringperiods when the pilot burner only is in operation.

The present invention provides a gas-fired water heater wherein theinlet and exhaust conduits extend horizontally or substantiallyhorizontally therefrom and that an extraction fan is incorpororated inthe exhaust conduit to draw combustion products from the combustionchamber and to expel said combustion products to atmosphere through theexhaust conduit.

The present invention further provides a gas-fired water heater asdescribed above wherein the circuit containing the extraction fanincludes electrical switching means adapted to control the volumetricair delivery rate of the fan in such a manner that the throughput of thefan required for operation of the main burner is reduced when gas issupplied to the pilot burner only.

A preferred gas-fired water heater in accordance with the presentinvention will now be described by way of example with reference to theaccompanying diagrammatic drawings in which:

FIG. 1 is a vertical cross-sectional view of the heater, and

FIG. 2 depicts an electrical circuit diagram relating to the heateradapted for space heating purposes by means of a conventional small borehot water circuit.

Referring 110W to FIG. 1, the Water heater comprises a rectangularbox-like combustion chamber 1 having an open bottom, four vertical sidepanels 2 and a top panel 3 provided with a circular aperture 4 in itscentre. Five bi-metallic finned heat-exchanger water tubes 5 areprovided longitudinally across the combustion chamber and are connectedtogether in series configuration by means of 180 U-shaped connectionpieces (not shown) situated externally of the combustion chamber. Thusthe flow of water passes five times through the appliance between inletand outlet connections (not shown) secured to the left-hand bottom andtop tubes 5 respectively. The burner unit comprises a main burnerconstituted, in simplified form, by a pair of burner rails 6 and 7connected by a cross pipe 8 to a gas supply pipe 9 via asolenoid-operated gas valve 26, and a continuously burning pilot light9a which is supplied from the gas supply at a point upstream of thevalve 26 by means of a pipe 9b.

The combustion chamber, heat exchanger assembly and burner unit areenclosed within a sealed casing 10 which is spaced from the combustionchamber 1 so as to form vertical air ducts 11 and 12, and upper andlower air chambers 13 and 14 respectively.

The casing is supported upon a pair of brackets (one of which is shownat 15) which are mounted within a room on the inside face of a cavitybrick wall 16.

A pair of juxtapositioned horizontal rectangular conduits 17 and 18 areconnected to the side of the casing and pass through an aperture formedin the wall 16 to a louvred terminal 19 as shown. The inlet conduit 17is provided with upwardly directed louvres and serves to admit air intothe upper air chamber 13, and the exhaust conduit 18 is provided withdownwardly directed louvres and serves as an exhaust exit for thecombustion gases from combustion chamber 1. The conduit 18 passesthrough the external wall of the casing 10 and communicates with thesnail housing 20 of a centrifugal fan having a fan impeller 21 fast withthe driving shaft of an electric motor 22. The eye intake of theimpeller is positioned above the aperture 4 in the top panel 3 of the 4combustion chamber. The electric motor is situated above the snailhousing 20 by brackets (not shown) within the upper air chamber 13.

Mains current supply is applied to the heating apparatus at L and N onthe left-hand side of the diagram. The LIVE supply L is fed through afuse 23, the contacts of a clock programmer 24, the contacts of an airthermostat 25, to three electrical devices connected in parallel andthence back to the NEUTRAL supply N. The electrical devices are asolenoid-operated gas valve 26 for controlling the flow of gas to themain gas burner from the gas supply pipe 9, a centrifugal water pump 27adapted to circulate hot water through the heatexchanger water tubes 28,and the coil windings 29 of a relay 30 having single-pole change-overcontacts. Independently of the above circuit the windings 31 of theclock programmer 24 are connected to the NEUTRAL supply and additionallyas the air thermostat 25 as illustrated is of the accelerated type, aresistance heater 32 is provided between the fixed contact of the sameand the NEUTRAL supply.

The driving motor 22 of the air fan 21 is connected from the unswitchedLIVE supply through the contacts of the relay 30, back to the NEUTRAL.It will be noted that the change-over contacts of the relay 30 connectto the air fan driving motor 22 via a 1500i) resistor 33 when the relayis de-energised, and alternatively by means of a direct wire 34 when itis energised. Thus it will be appreciated that when the air thermostat25 is closed and the gas valve 26 and water pump 27 are operative, therelay will always be energised and consequently the air fan drivingmotor 22 will run at mains potential. Conversely, when the thermostat 25is open and the gas valve 26 and water pump 27 are inoperative the airfan driving motor 22 will run at reduced speed. It will be apparent thatthis latter condition will prevail regardless of the operation of theprogrammer 24 or the air thermostat 25, with the result that a small airflow will always be maintained through the heater and the aforementionedproblems are substantially overcome. I

The air-exhaust flow through the heater is indicated by a procession ofarrows and is as follows. Assuming that the air thermostat 25 demandsheat, gas supply is admitted to the burner rails 6 and 7 where it isignited by the pilot light. Simultaneously with the admission of gas anelectric current supply is connected to the relay 29, the effect ofwhich is to direct current at mains potential to the air fan drivingmotor 2. The resulting operation of the fan expels the combustionproducts through the exhaust conduit 18 and combustion products aredrawn into the eye of the impeller 21 through the aperture 4. The effectof this is to create negative pressure within the combustion chamber 1and, to retain equilibrium, atmospheric air is drawn through the intakeconduit 17 into the upper air chamber 13, downwardly through thevertical air ducts 11 and 12 and finally into the lower open bottom ofthe combustion chamber.

It will be appreciated that the fan driving motor will be cooled byincoming air and also that if any leaks should occur within the wall ofthe casing 10 atmospheric air from the room will enter into the case;thus it will be quite impossible for injurious products of combustion toleak into the room.

The circuit diagram must be regarded as a simple arrangement and in thecase of dual-purpose heat supply functions, i.e. to provide for spaceheating and consumable hot-water requirements, additional circuitry andrelays will be necessary; however, the essential integers formulatingthe invention will always be carried out in a manner similar to thatdescribed above. Furthermore it must be understood that the arrangementof the boiler as shown in FIG. 1 includes various conventionaltemperature control devices which are not specifically indicated orreferred to. These comprise essentially a modulating type gas flowcontrol valve disposed between the valve 26 and the main burner unitwhich is capable of being influenced in accordance with the water flowtemperature, a pilot-light flame-failure safety device and also one ormore excess temperature cut-out devices to safeguard the applianceagainst abnormal temperatures that may be created by component failureor water fiow obstruction, for example.

We have found that using a particular air fan as fitted to a waterheater of 50,000 B.t.u./hr. thermal output, a 15,0000 resistor reducedthe effective voltage, as applied to the fan, from a mains potential of250 v. to 105 v. The effect of this was to reduce the throughput of thefan from 16 cu. ft./min. to 3 cu. ft./min. at rotational speeds of 2500rpm. and 500 rpm. respectively. We have found that a throughput of 3 cu.ft./min. effectively prevents formation of condensation products andadditionally has enhanced the reliability and quietness of operation ofboth the pilot and main burners.

Additionaly, because the air fan is continually in motion, it is capableof accelerating up to its full working speed in an extremely short time,whereas in the known arrangements this can occupy several minutes owingto inherent oil and other mechanical drag conditions associated withstarting from cold.

What is claimed is:

1. A room-seal gas-fired water heater comprising a heater assemblyincluding a housing defining a combustion chamber, an air inlet port insaid housing, an exhaust outlet port in said housing spaced from saidair inlet port, a burner unit including an intermittently operable mainburner and a continuously burning pilot burner mounted in saidcombustion chamber, a tubular heat exchanger supported in saidcombustion chamber betwen said burner unit and said exhaust outlet port,a casing sealingly enclosing said heater assembly, first and secondconduits extending horizontally from said casing and connected theretoto define an air inlet and exhaust outlet respectively, the outer end ofeach conduit being open to the atmosphere and the inner end of saidfirst and second conduits being placed in communication with said airinlet port and said exhaust outlet port respectively, said outer endsbeing arranged closely and parallel together to provide a balanced-flue,rotary extraction fan means disposed in said second conduit forexpelling combustion products drawn from said combustion chamber,electric motor means for rotating said extraction fan means and controlmeans adapted to control the rate of flow of the combustion productsfrom the apparatus so as to provide a first effective volumetricthroughput when both the main and pilot burners are in operation, and

a normally operating second effective volumetric throughput less thanthe said first throughput for coperation with the pilot burner only.

2. Gas-fired water heating apparatus according to claim 1 wherein thesaid control means comprise an electrical switch adapted to selectivelyapply a first voltage to the electric motor means thereby to provide thesaid first throughput and a second voltage lower than the first voltageto the electric motor means to provide the said second throughput.

3. Gas-fired water heating apparatus as claimed in claim 2 wherein thesaid second voltage is derived by bringing a resistor in the circuitcontaining the said electric fan means.

4. Gas-fired water heating apparatus as claimed in claim 3 wherein theelectrical switch comprises an electromagnetic relay having a coil whichis energised simultaneously with a solenoid valve adapted when energisedto admit gas to the main burner, the arrangement being such that whenthe relay coil is de-energised the said second voltage is applied to theelectric fan means.

5. Gas fired water heating apparatus as claimed in claim 2 wherein theelectrical switch comprises an electromagnetic relay having a coil whichis energised simultaneously with a solenoid valve adapted when energisedto admit gas to the main burner, the arrangement being such that whenthe relay coil is de-energised the said second voltage is applied to theelectric fan means.

6. Gas-fired water heating apparatus according to claim 1 wherein saidhousing is disposed upright within said casing and said air inlet portis in the form of an open bottom on said housing, said exhaust outletport being at the top of said housing, and said extraction fan meansbeing aligned with said exhaust outlet port for receiving exhaust gasesdirectly therefrom.

7. Gas-fired water heating apparatus according to claim 6 wherein saidelectric motor means are mounted in the path of air flowing through saidair inlet.

References Cited UNITED STATES PATENTS 1,892,188 12/1932 Goodridge236-16 2,246,566 6/1941 Ames et a1. 236-1AUX 2,635,813 4/1953 Schlenz2361A 2,685,917 8/1954 Perry 236-1AX 2,958,377 11/1960 Laing 431-20XEDWARD J. MICHAEL, Primary Examiner

